The invention relates to an internal combustion engine having a control device arranged to provide a heating mode of the internal combustion engine, and a method for controlling an internal combustion engine.
The invention is applicable on different types of vehicle and engine, in particular working machines within the fields of industrial construction machines and construction equipment, such as wheel loaders and articulated haulers. Although the invention will be described with respect to a wheel loader, the application of the invention is not restricted to this particular machine, but may also be used in other vehicles, such as trucks and buses for instance.
It is difficult to warm up a diesel engine running in a low load operation, particularly in a cold environment. The use of an engine having a low temperature will increase the fuel consumption and the wear of the engine. In addition, the exhaust gas temperature will also be low and that makes an exhaust aftertreatment system ineffective or not usable at low load.
In order to solve the problems related to a low exhaust gas temperature some engines have certain operation modes for rapidly raising the exhaust gas temperature of the engine and thereby enabling the use of exhaust aftertreatment system, such as Selective Catalytic Reduction (SCR).
Document U.S. Pat. No. 8,091,340 discloses a method of controlling the intake of an internal combustion engine where a greater proportion of the total feed is admitted into one group of cylinders than in another group of cylinders to achieve an increased exhaust gas temperature. During some operation conditions the efficiency of this method is however not sufficient and/or the method involves an increased fuel consumption.
It is desirable to provide an internal combustion engine and a method where the engine temperature as well as the exhaust gas temperature can be raised in an efficient way during a heating mode.
By the provision of an internal combustion engine having a plurality of cylinders, where the internal combustion engine is provided with an arrangement for exhaust gas recirculation, and the plurality of cylinders are divided into a first group and a second group of cylinders, and the internal combustion engine has a control device arranged to provide a heating mode of the internal combustion engine where the first group cylinders are deactivated and the second group cylinders are activated, and in the heating mode the control device is further arranged to provide a higher proportion recirculated exhaust gas than inlet air to the first group cylinders, the engine can be run with a reduced amount of excessive air.
By the definition that the first group cylinders will be deactivated is meant that these cylinders are non-firing cylinders in the heating mode. Accordingly there is not any fuel introduced into the first group cylinders (or only a negligible fuel amount not sufficient to achieve ignition of the gas in the cylinder is introduced). Thus, while not increasing the total fuel consumption an increased amount of fuel can be introduced into the activated second group cylinders, i.e. the working cylinders or firing cylinders, to rapidly increase the temperature and maintain the engine load.
The invention is based on the insight that excessive air flow (very high lambda) at low engine load will act as a cooler on the engine, in particular on the non-firing cylinders, and will counteract an increased exhaust gas temperature.
By the provision of a higher proportion recirculated exhaust gas than inlet air to the first group cylinders in the heating mode, the cold air mass flow through the engine can be significantly reduced. This will give increased exhaust temperature and heat input to the engine cooling system and will decrease the requisite time for achieving the desired engine and exhaust temperatures. Although the cylinders could be controlled individually, in the heating mode the control device is preferably arranged to provide a higher proportion recirculated exhaust gas than inlet air to each cylinder of the first group cylinders. In other words; for each first group cylinder the amount of recirculated exhaust gas is more than 50% of the total gas volume introduced into the cylinder and the amount of inlet air is less than 50% of the total gas volume introduced into the cylinder.
This in turn will reduce the fuel consumption due to a decreased idle time and less friction between the engine components. Normal engine temperature can be maintained at colder climate. Other less fuel efficient warm up methods (heat modes) can be avoided. These other methods often depend on throttling of the gas flow at the inlet or exhaust side, or on reduction of the expansion work by either phasing the heat release later or opening the exhaust valve earlier.
Furthermore, the use of a NOx agent as urea solution is possible also at low load or idle operation with reduced risk of crystallization. By a higher idle temperature the light-off temperature of a Diesel Oxidation Catalyst (DOC) can be achieved faster. Also regeneration of soot-filter could be possible at idle operation if the temperature is increased.
According to a preferred embodiment of the invention, in the heating mode the control device is arranged to provide more than 60% recirculated exhaust gas and less than 40% inlet air to the first group cylinders, suitably more than 70% recirculated exhaust gas and less than 30% inlet air, and preferably more than 80% recirculated exhaust gas and less than 20% inlet air, and more preferably more than 90% recirculated exhaust gas and less than 10% inlet air, and most preferably more than 95% recirculated exhaust gas and less than 5% inlet air to the first group cylinders. Hereby the heating of the engine can be performed with very high efficiency.
Ideally the control device is arranged to stop the inlet air flow to the first group cylinders and to provide substantially only recirculated exhaust gas to the first group cylinders in the heating mode, i.e. the amount of recirculated exhaust gas introduced into the respective cylinder of the first group cylinders is preferably substantially 100% of the total gas volume introduced into the cylinder.
According to a further preferred embodiment of the invention, where the control device comprises a valve for limiting or preventing a flow of inlet air to the first group of cylinders while allowing a flow of inlet air to the second group of cylinders in the heating mode, and preferably where the internal combustion engine has an inlet air manifold for providing air to the plurality of cylinders and said valve for limiting or preventing a flow of inlet air to the first group of cylinders is arranged inside the inlet air manifold for dividing the cylinders into the first group and second group of cylinders, a non-complicated, compact and cost efficient design of the engine can be obtained.
According to a further embodiment of the invention, where the internal combustion engine has a cooler for cooling the recirculated exhaust gas before the recirculated exhaust gas is introduced into the first group cylinders in the heating mode, the temperature of the exhaust gas can be controlled to optimize the heating of the engine without introducing gas having such a high temperature that the cylinders could be damaged.
The invention is preferably applied to an internal combustion engine that normally has a great excess of air (high lambda), particularly at low engine load, since the effect of the invention is very significant when applied to these engines. Accordingly, the engine is preferably a compression-ignition engine, such as a diesel engine, though the invention can also be applied to other kinds of engine, such as for example Otto cycle lean burn engines.
According to a further aspect, the invention also relates to a method for controlling an internal combustion engine according to claim 14. The same advantages as discussed above with reference to the internal combustion engine can be reached by the method according to the invention.
Further advantages and advantageous features of the invention are disclosed in the following description and in the dependent claims.